1. Field of the Invention
The present invention relates to a line bypass system for a radio base station (hereinafter referred to as a CPRI radio base station) for adopting the CPRI (Common Public Radio Interface) as an open interface in the radio base station where the control unit and the radio unit are named as an REC (radio equipment control) and an RE (radio equipment) in the CPRI respectively, and both units are disposed separately and connected by an optical fiber line.
2. Description of the Related Art
The common mounting mode for a recent radio base station is a one-to-n connection form in which a radio control unit (REC) and n radio units (REs) located in separate places are connected by optical fibers. There are increasing cases in which the Common Public Radio Interface (CPRI) is used in an interface unit between the REC and REs. The detailed contents of the CPRI can be acquired by accessing the non-patent document described below.
FIG. 1 is a schematic chart of the radio base station in which the above-mentioned CPRI is adopted as an internal interface.
A radio base station (100) is configured by a REC (101), n REs (120), and a CPRI link (110) by the optical fiber connecting each RE (120) with the REC (101). The RE (120) is provided in, for instance, an underground mall or similar location, and a mobile terminal (140) can be used even when it is located in a place where radio waves cannot reach from the point where the REC (101) is mounted.
With the above-mentioned configuration of the radio base station (100), when there occurs a disconnection of an optical fiber between the REC and an RE, the RE that is connected by the disconnected optical fiber cannot transmit a signal (user data, monitor/control signal, etc.) to or receive it from the REC, and enters the inoperable state, and the mobile terminal (140) enters the intra-cell wait status, thereby disabling communications to be performed.
Normally, to avoid the above-mentioned problems, a plurality of optical fibers of an equal transmission capacity are mounted between the REC and the RE so that the optical circuit can have a redundant configuration. However, since a plurality of optical fibers are used, the mounting cost inevitably increases.
Furthermore, as shown in FIG. 2, when there occurs a fault in a CPRI link #2 (110′) between an RE#2 (120′) and the REC (101), and if the above-mentioned problem is to be solved by transmitting and receiving data between the RE#2 (120′) and the REC (101) through the communication line (130) and the RE#1 (120), then the data between the REC (101) and the RE#1 (120) and the data between the REC (101) and the RE#2 (120′) flow through the CPRI link #1 (110). Therefore there arises the problem that the transmission capacity of the optical circuit between the REC (101) and the RE#1 (120) has to be increased. As other measures against a fault of a communication system, for instance, there are the techniques described in the following patent documents 1 and 2.
The technique disclosed by the patent document 1 is measure against a fault by what is called an N+1 configuration. Although the N+1 configuration is more economical than the duplex configuration, a standby link and one RE has to be provided for N links and N REs if it is applied to the CPRI link of the CPRI radio base station. However, since each RE is provided in a different place, and it is not predictable that a fault occurs in the link of which RE, the N+1 configuration cannot be adopted to the CPRI link fault in the CPRI radio base station.
What is disclosed by the patent document 2 relates to the ATM exchange network, and a standby connection is established or reserved in case of a fault of the current connection in operation. That is, it originally relates to the technique for an exchange network in which there are a plurality of connection routes between nodes, and cannot be applied to a 1-to-N connection such as a CPRI radio base station and the like.    [Patent Document 1] Japanese Published Patent Application No. H08-149180    [Patent Document 2] Japanese Published Patent Application No. 2001-298461    [Non-patent Document 1] CPRI Common Public Radio Interface (http:/www.cpri.info/spec.html)